People ask me fairly often why my daughter wears sunglasses. Is there something wrong with her eyes? No. Does she like to wear them? Not particularly. Is it because it's so cute? That's good incentive, but it's not the main reason. I make her wear them, and she isn't allowed to take them off when we're outside, because I don't want her eyes to be damaged by sunlight.
It's amazing to me; I'll see parents slathering sunscreen on their kids, putting on hats for good measure, and completely neglected those precious jewels. I'm guessing it's mostly out of ignorance, as whenever I explain, people tell me how much sense it makes. Of course they need protection. Many adults put on sunglasses because brightness hurts their own eyes and don't think to put them on children because there's no way for the child to communicate discomfort.